1. Field of the Invention
The present invention relates to a transmission apparatus, a method for controlling a transmission apparatus, and an information communication system.
2. Description of the Related Art
Conventionally, there has been proposed an information communication system by which a transmission apparatus such as a digital camera or a digital video camera and a receiving apparatus such as a television are connected via wireless communication. In this information communication system, it is envisaged that a camera and a television be connected via wireless communication, for example, in the millimeter wave band, or more specifically, in the 60-GHz band.
Wireless communication in the 60-GHz band provides high-capacity communication with a maximum speed of 5G bps. Through wireless communication in the 60-GHz band, moving images (hereinafter referred to as “1080p”) having a pixel size of 1920×1080 with a frame frequency of 59.94 Hz can be transmitted via wireless communication. In a conventional information communication system using wireless communication in the 60-GHz band, a camera transmits the 1080p moving image to a television via wireless communication, so that the television reproduces the 1080p moving image. The 1080p moving image is configured to output normal image and voice data as well as still picture data as frame data.
Wireless communication in the 60-GHz band has very high directivity due to its short radio wavelength and high linear progressivity characteristics. Hence, the positional relationship between a transmission apparatus and a receiving apparatus or the condition of the transmission path have a greater impact on data transmission. For the physical layer of wireless communication in the 60-GHz band, there are two modes proposed for this: one is a single-carrier mode to be used in a point-to-point connection and the other is a multi-carrier mode for OFDM (orthogonal frequency division multiplex).
In view of the characteristics of high directivity of wireless communication in the 60-GHz band, the IEEE 802 Committee obligates implementing a common mode so as to ensure minimal communication between communicating devices. As disclosed in IEEE802.15-07-0934-01-003c, p12-14, p21-24, and p51-54, the common mode refers to the transmission mode using a single carrier wave with relatively low speed (about 50 Mbps), which is for use in obtaining or authenticating status information of the devices and transmitting a beacon signal.
Conventionally, television apparatuses with a power saving function are known. In the television apparatuses with the power saving function, if no signal input has been received from an external device such as a recorder for a predetermined period of time, a system power circuit is switched off or a monitor is turned off, whereby power consumption is reduced. As disclosed in Japanese Unexamined Patent Application Publication No. 5-236394, another method is such that if no input signal has been received for a predetermined period of time, an input switching circuit is switched to a terminal receiving a signal input, e.g., to a normal broadcast input, whereby a predetermined image is displayed on the screen. Since a user can view the predetermined image displayed and recognize that the power the television apparatus is not switched-off, whereby forgetting to turn the power off is prevented. In this way, such television apparatuses are common which, in a state of the absence of signal input from the signal input source, execute an operation such as turning the power off or turning off the monitor after a predetermined period of time, or switching to the other signal input source as the no-signal condition avoidance operation.
However, a conventional information communication system by which a transmission apparatus and a receiving apparatus are connected via wireless communication in the 60-GHz band has problems described below. When a user begins to view an image after the establishment of a connection between a transmission apparatus such as a camera and a receiving apparatus such as a television, the user may move the camera for operation. Under such circumstances, because of the high directivity of wireless communication in the 60-GHz band, communication may be terminated by the change of the positional relationship between the transmission apparatus and the receiving apparatus. In particular, when the transmission apparatus is a device such as a digital camera or a digital video camera, on the assumption that a user may pick up such device with his/her hands for operation, such problems become marked.
In such cases, the television detects the absence of signal input from the camera and executes a control operation for avoiding a no-signal condition such as turning off the power of the receiving apparatus after the elapse of a predetermined period of time. On the other hand, assume that in order to start viewing again, after the completion of an operation of the camera, a user places the camera at the original position, that is, the position where the connection has been established before the user has picked up the device. However, the television may have already been shifted to a power-off state at that point as a result of the avoidance of a no-signal condition. For this reason, the user may need to turn on the power of the television again, to handle the input switching process, or to re-establish the wireless connection settings. Consequently, there arises a problem in that viewing an image cannot readily be continued.